Power shears have been used for a number of years for various heavy duty cutting and shearing tasks. For example, they are used in demolition work to reduce materials, such as concrete and steel, to smaller size chunks suitable for removal from a demolition site. In conventional power shears, each of two opposing jaws has a shear knife removably positioned in a knife seat. Typically, a shear knife has a substantially rectangular configuration with at least two, usually four, cutting edges. It is made of an extremely hard, wear resistant material so that each of the four cutting edges may be sharpened to provide shearing action in cooperation with a cutting edge of a shear knife on an opposing jaw. When a cutting edge wears out, the shear knife may be removed from its knife seat, reoriented, and replaced in the knife seat with a different edge serving as the cutting edge. When all four cutting edges are worn, the shear knife typically must be taken to another location for repair. The repair involves welding on and regrinding each of the cutting edges. To avoid delays in the demolition work, the shear knife that has been removed from the demolition site must be replaced with a new shear knife.
In order to provide four cutting edges, the entire body of the shear knife must be made from an extremely hard, wear resistant material. Once a shear knife can no longer be repaired, the high cost of the material from which it is made adds considerably to the expense of replacing the entire shear knife. The high cost and time consuming nature of the repair operation further adds to the expense of the conventional shear knife.
FIG. 1 illustrates a common type of known power shear 2. The shear 2 has a stationary jaw 4 and a pivotable jaw 6 pivotably connected to the stationary jaw 4 at a pivot connection 8. The shear 2 is mountable on a piece of heavy equipment, such as a backhoe. The hydraulic system of the backhoe may be used to power the shear 2. Each jaw 4, 6 carries one or more shear knives. An L-shaped knife seat 10 (FIG. 1A) is provided for receiving each shear knife. Referring to FIG. 1, the stationary jaw 4 has a knife seat that receives a shear knife 12, and the pivotable jaw 6 has a knife seat that receives an opposing shear knife 14. The two shear knives 12, 14 have confronting surfaces 16, 18, respectively, that face or confront each other. The exposed outer edges 20, 22 of the confronting surfaces 16, 18 form cutting edges. Each shear knife 12, 14 is removably secured in its knife seat by a plurality of fasteners 24. When the pivotable jaw 6 is pivoted relative to the stationary jaw 4, the structural elements being demolished are gripped between the two jaws 4, 6 by the confronting surfaces 16, 18. The pivotable jaw 6 is received down into a slot formed by the stationary jaw 4 to shear the structure gripped by the jaws 4, 6. The shearing action is provided by the shear knives 12, 14, and specifically by their cutting edges 20, 22, as the pivotable cutting edge 22 moves toward and past the stationary cutting edge 20 and into the recess.
The cost of the conventional plural-cutting-edge shear knife is further increased by the need to replace the entire shear knife in order to provide a cutting edge of a different material. In demolition work, various types of materials are broken up. For example, both concrete and steel may need to be sheared during the demolition of a building having reinforced concrete structures. A cutting edge material suitable for use in shearing steel is generally not suitable for concrete. Thus, the entire shear knife must be replaced for optimal efficiency in shearing the different materials. The additional expense that this entails adds to the cost of the demolition operation. Moreover, the choice of materials may be limited by a lack of compatibility of some cutting materials with the material of the power shear knife seat.